表格在同一页面上提交后如何显示消息

Question

<?php
session_start();
include("includes/config.php"); 

if(isset($_POST['submit'])){
    
    if (empty($username)){
        $error1 = "Please enter username.";
        header("location: index.php");

    }
    
    $username=mysqli_real_escape_string($con,$_POST['username']);
    $password=mysqli_real_escape_string($con,$_POST['password']);
    
    $sql="select * from admin_user where username='$username' and password='$password'";
    
    $res=mysqli_query($con,$sql);
    if (mysqli_num_rows($res)>0){
        
       session_start();
       $_SESSION["username"] = $username;
       $_SESSION["id"] = $id;
       $_SESSION['admin']['status']= true ;

      header("location: dashboard.php");
    }else{
        $unsucess = "Invalid username or password.";
header("location: index.php");
    }
        
        
}
?>

                    

<?php if(!empty($error1)) {?>
   <p><?php echo $error1; ?></p>
<?php } ?>
                       
                           <form method ="post">
                              <div class="mb-3">
                                 <label for="username" class="form-label">Username*</label>
                                 <input type="text" name="username" class="form-control" id="username" placeholder="Enter username">
                              </div>
                              <div class="mb-3">
                           
                                 <label class="form-label" for="password-input">Password*</label>
                                 <div class="position-relative auth-pass-inputgroup mb-3">
                                    <input type="password" name="password" class="form-control pe-5" placeholder="Enter password" id="password">
                                    <button class="btn btn-link position-absolute end-0 top-0 text-decoration-none text-muted shadow-none" type="button" id="password-addon"><i class="ri-eye-fill align-middle"></i></button>
                                 </div>
                              </div>
                              <div class="mt-4">
                                 <button class="btn btn-success w-100" name="submit" type="submit">Sign In</button>
                              </div>
                   
                           </form>

我在同一页面上通过邮政方法提交表单。提交表格后，我检查一个条件，如果用户名为null，则显示$ error1 =“请输入用户名”;在表格之上的消息。我面临的问题是删除标头时（“位置：index.php”）;在身体部分上正确显示的消息。但是，如果添加标头（“位置：index.php”）;对于刷新页面，$ error1由于页面刷新而未显示。但是没有标头（“位置：index.php”）;浏览器在刷新页面期间给出消息（要显示此页面，Firefox开发人员版本必须发送将重复任何动作（例如搜索或订单确认）的信息。）如何正确显示消息的任何建议以及如何防止信息提交表格（包括标题）（“位置：index.php”）之后重复采取行动；额外。 <代码>在此处输入代码

Answer 1

在会话中添加错误，并检查会话ISSET值ECHO错误和未设置错误会话会话

<?php
session_start();
include("includes/config.php"); 
if(isset($_POST['submit'])){
    
    if (empty($username)){
        $_SESSION['error1'] = "Please enter username.";
        header("location: index.php");
    }
    
    $username=mysqli_real_escape_string($con,$_POST['username']);
    $password=mysqli_real_escape_string($con,$_POST['password']);
    
    $sql="select * from admin_user where username='$username' and password='$password'";
    
    $res=mysqli_query($con,$sql);
    if (mysqli_num_rows($res)>0){
        
       session_start();
       $_SESSION["username"] = $username;
       $_SESSION["id"] = $id;
       $_SESSION['admin']['status']= true ;

      header("location: dashboard.php");
    }else{
        $_SESSION['error1'] = "Invalid username or password.";
        header("location: index.php");
    }
        
        
}
?>

                    

<?php if(isset($_SESSION['error1'])) {?>
   <p><?php echo $_SESSION['error1']; ?></p>
<?php unset($_SESSION['error1']); } ?>
                       
                           <form method ="post">
                              <div class="mb-3">
                                 <label for="username" class="form-label">Username*</label>
                                 <input type="text" name="username" class="form-control" id="username" placeholder="Enter username">
                              </div>
                              <div class="mb-3">
                           
                                 <label class="form-label" for="password-input">Password*</label>
                                 <div class="position-relative auth-pass-inputgroup mb-3">
                                    <input type="password" name="password" class="form-control pe-5" placeholder="Enter password" id="password">
                                    <button class="btn btn-link position-absolute end-0 top-0 text-decoration-none text-muted shadow-none" type="button" id="password-addon"><i class="ri-eye-fill align-middle"></i></button>
                                 </div>
                              </div>
                              <div class="mt-4">
                                 <button class="btn btn-success w-100" name="submit" type="submit">Sign In</button>
                              </div>
                   
                           </form>